Due to new electricity generation and supply schemes, optimising cost and return in greenhouse production could be achieved with interruptive schemes for supplementary lighting (SL). We analysed the effect of interrupted SL (ISL) on both the cost of electricity and crop yield of tomato cultivation during a winter in Brandenburg, Germany (LAT 52°N). We applied SL for 60 days to a tomato crop (cv. Komeett) with two nighttime regimes of nine hours using high pressure sodium lamps (HPSL; 400 W and 210 μmol m–2 s–1) resulting in equivalent daily light integral (DLI, mol m–2 day–1). CO2 assimilation of the crop stand was measured either continuously in four airtight gas exchange greenhouse compartments (28.8 m2 each) or from a sampling of total dry mass. Measurements were used to evaluate the predictions of an existing deterministic photosynthesis model. Results indicate: 1) continuously measured crop net photosynthesis (Pn) overestimated the total CO2 assimilation when measured as crop dry matter at only 1.7%, and 2) an ISL regime had only a low influence on total dry mass formation, presenting 7.6% higher total dry matter in comparison to the model results. It is concluded that 1) continuous measurements of Pn in a daylit environment can be used as a dry mass increase indicator, 2) ISL can be applied without losses in tomato yield, and 3) the existing tomato crop photosynthesis model was not suitable for ISL control. Thus, price optimised ISL can be applied with no negative effect only by looking at electricity prices.
Long term measurements of carbon dioxide gas exchange under interrupted supplemental lighting on greenhouse tomato crops
Ramírez, T.; Kläring, H.-P.; Körner, O. 2019. Long term measurements of carbon dioxide gas exchange under interrupted supplemental lighting on greenhouse tomato crops. Biosystems Engineering, 187, 69-80.